<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .a{
            border: 1px solid #333;
            width: 100px;
            height: 100px;
            text-align: center;
            line-height: 100px;
        }
        .s{
            display: inline-block;
            vertical-align: middle;
            width: 40px;
            height: 40px;
            background-color: pink;
        }
    </style>
</head>
<body>
    <div class="a">
<div class="s">

</div>
    </div>
</body>
</html>